What EZ is talking about here:
Bo:
3 years, DBs (SF)
3 years, LBs (NE)
3 years, LBs (GB)
After which Bo got some heavy-hitting recommendations (Pete Carroll too, if I'm not mistaken) and got his shot. Bo really worked hard and shot up the ladder in those 9 years (one year before which he spent scouting for SF), to get his shot at a big-time DC position where he was charged to fix a sagging defense. With his resume, Bo was a hot young assistant at that time, and a rising star in the profession - rather than a proven guy or whatever.
Frost:
2 years, LBs (Northern Iowa)
2 years, WRs (Oregon)